The hardest natural mineral on Earth is diamond. Composed of carbon atoms arranged in a crystal lattice structure, diamonds are renowned for their exceptional hardness and are often used in cutting tools and jewelry. They can only be cut or scratched by other diamonds. Diamonds form under extreme pressure and temperature conditions deep within the Earth's mantle over billions of years. Their unique properties, including brilliance and durability, make them highly prized in various applications, from industrial uses to becoming symbols of luxury, particularly in engagement rings.